Visibility of Lights

Rule text#

The lights prescribed in these Rules (Subpart C) shall have an intensity as specified in Annex I to these Rules (33 CFR part 84), so as to be visible at the following minimum ranges:

(a)In a vessel of 50 meters or more in length:

(i)A masthead light, 6 miles;

(ii)A sidelight, 3 miles;

(iii)A sternlight, 3 miles;

(iv)A towing light, 3 miles;

(v)A white, red, green or yellow all-round light, 3 miles; and

(vi)A special flashing light, 2 miles.

(b)In a vessel of 12 meters or more in length but less than 50 meters in length:

(i)A masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles;

(ii)A sidelight, 2 miles;

(iii)A sternlight, 2 miles;

(iv)A towing light, 2 miles;

(v)A white, red, green or yellow all-round light, 2 miles; and

(vi)A special flashing light, 2 miles.

(c)In a vessel of less than 12 meters in length:

(i)A masthead light, 2 miles;

(ii)A sidelight, 1 mile;

(iii)A sternlight, 2 miles;

(iv)A towing light, 2 miles;

(v)A white, red, green or yellow all-round light, 2 miles; and

(vi)A special flashing light, 2 miles.

(d)In an inconspicuous, partly submerged vessel or objects being towed:

(i)A white all-round light, 3 miles.

(ii)[Reserved] [USCG-2012-0102, 79 FR 37912, July 2, 2014, as amended by USCG-2012-0102, 79 FR 68621, Nov. 18, 2014; USCG-2020-0304, 85 FR 58277, Sept. 18, 2020]

(a)In a vessel of 50 meters or more in length:

(i)A masthead light, 6 miles;

(ii)A sidelight, 3 miles;

(iii)A sternlight, 3 miles;

(iv)A towing light, 3 miles;

(v)A white, red, green or yellow all-round light, 3 miles; and

(vi)A special flashing light, 2 miles.

(b)In a vessel of 12 meters or more in length but less than 50 meters in length:

(i)A masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles;

(ii)A sidelight, 2 miles;

(iii)A sternlight, 2 miles;

(iv)A towing light, 2 miles;

(v)A white, red, green or yellow all-round light, 2 miles; and

(vi)A special flashing light, 2 miles.

(c)In a vessel of less than 12 meters in length:

(i)A masthead light, 2 miles;

(ii)A sidelight, 1 mile;

(iii)A sternlight, 2 miles;

(iv)A towing light, 2 miles;

(v)A white, red, green or yellow all-round light, 2 miles; and

(vi)A special flashing light, 2 miles.

(d)In an inconspicuous, partly submerged vessel or objects being towed:

(i)A white all-round light, 3 miles.

(ii)[Reserved] [USCG-2012-0102, 79 FR 37912, July 2, 2014, as amended by USCG-2012-0102, 79 FR 68621, Nov. 18, 2014; USCG-2020-0304, 85 FR 58277, Sept. 18, 2020]

Why it shows up on the exam#

The number examiners reach for is 6: the only 6-mile light in the rule is the masthead light of a vessel 50 metres or longer. The second favourite is the 20-metre exception hidden inside the 12-to-50-metre band, which knocks the masthead from 5 miles down to 3. Note also that sidelights always have the shortest range of any light on the vessel — 1 mile below 12 metres.

Exam checkpoints#

1. 1.

   50 m and over

   Masthead 6 nm · rest 3 nm

   Masthead light 6 miles; sidelights, sternlight, towing light and any white, red, green or yellow all-round light 3 miles. This is the only place a 6-mile range appears.

2. 2.

   12 m to under 50 m

   Masthead 5 nm · rest 2 nm

   Masthead light 5 miles, except that where the vessel is less than 20 metres in length the masthead light need only be visible 3 miles. Sidelights, sternlight, towing light and all-round lights 2 miles.

3. 3.

   Under 12 m

   Sidelights only 1 nm

   Masthead light 2 miles; sidelights 1 mile; sternlight, towing light and all-round lights 2 miles. The 1-mile sidelight is the shortest range in the rule.

4. 4.

   Inconspicuous object

   White all-round 3 nm

   An inconspicuous, partly submerged vessel or object being towed shows a white all-round light visible at 3 miles — the same range a 50-metre vessel's sidelights must carry.

Inland-specific notes#

Inland Rule 22 (33 CFR §83.22) carries the same ranges as COLREGs Rule 22. There is no separate band for vessels of 100 metres or more in either rulebook — the 50-metres-or-more band covers every larger vessel, which catches out candidates who assume the biggest ships must have their own row.

Rule 22 — common exam questions#

How far must a masthead light be visible?

It depends on length. Under Rule 22 a vessel of 50 metres or more must show her masthead light 6 miles; a vessel of 12 metres or more but less than 50 metres, 5 miles — reduced to 3 miles if she is under 20 metres; and a vessel of less than 12 metres, 2 miles.

Which light has the shortest required range?

The sidelight. On a vessel of less than 12 metres the sidelights need be visible only 1 mile, against 2 miles for her masthead, sternlight, towing light and all-round lights. At every length band the sidelights are at or below the range of the other lights, which is why a small vessel's red and green are the first thing you lose at distance.

Is there a separate visibility range for ships over 100 metres?

No. Rule 22's largest band is 50 metres or more, and it applies to every vessel above that length, however big. Rule 33's sound-signal equipment does add a 100-metre threshold — that is where the gong appears — and the two rules are easy to conflate.

Are the Inland ranges different from the International ones?

No. 33 CFR 83.22 sets the same ranges as COLREGs Rule 22, so a memorised table serves for both rulebooks.

Authoritative source#

Source links checked against the current public rule corpus on 2026-07-26.

• 33 CFR §83.22 — the section this text comes from, with its neighbours.
• The Inland Navigation Rules are codified at 33 CFR Part 83 and are public domain. The international COLREGs text is published separately by the IMO.

Practice this rule#

One real exam question on this rule, cited to source. No sign-up.